The most common way to lock and unlock an access-controlling object such as a door is probably by using a mechanical key. This solution is cost efficient and easy to use, and a sophisticated mechanical lock is hard to force. However, there are two drawbacks with this solution: the user always has to bring the key and the key does not have any restrictions, i.e. it always works.
These drawbacks might seem like minor disadvantages, which might be true in situations with one user and one door, but in situations with a large number of users and a large number of doors the drawbacks are of considerable importance. In more particular, if a large number of users must have access to a large number of doors, a large number of keys has to be made for the different doors. This is not only unhandy but also a considerable security risk and costly.
Firstly, in order to reduce the security risk, some sort of key administration is necessary. This type of administration is costly.
Secondly, a user who receives a key might abuse it, and even if the user is a responsible person, the key might be stolen or lost. Since there are no built-in restrictions in a mechanical key the security risk becomes significant. Consequently, handing out a large number of keys is a security risk.
Thirdly, if one of the keys is lost or stolen the corresponding lock has to be substituted, as well as all the other corresponding keys, in order to maintain the security. The administration costs, locksmith costs and all interruptions due to these key substitutions imply considerable costs for a lost key.
A mechanical key system is hence not suitable for situations with a large number of users and a large number of doors. An example of such a situation is the elderly home care, where the domestic help personnel has a key to each of the caretakers. In order to solve this problem another type of locking system is necessary.
In WO 02/31778 A1 a wireless lock system is presented. When the lock of the system detects a nearby electronic key carried by a user, a random signal is generated. The key encrypts the signal and returns it to the lock. The lock decrypts the signal and compares it to the original to determine if the lock should be unlocked.
In order to function, the wireless lock system mentioned above must always establish a two-way wireless communication link between the key and the lock. This is a drawback, since the establishment of a two-way communication link is not made instantly. Hence, a user has to wait for a period of time until the establishment of the two-way communication link is completed, and thereafter the user has to wait until the comparison is completed. The present inventors have realized that if the wireless lock system in WO 02/31778 A1 is to be implemented with the de facto standard for short-range wireless data communication for mobile devices, namely RF communication in accordance with the Bluetooth™ standard on e.g. the 2.45 GHz ISM band, one must expect at least about 10 seconds, and possibly up to as much as 30 seconds, for the establishment of the two-way Bluetooth™ link alone; to this one must add the time required for performing the data exchange and comparison. Another drawback with the approach described in WO 02/31778 A1 is that the key will have to be implemented as a rather advanced, programmable wireless communication device, such as a high-end mobile telephone.
Users who are used to mechanical keys are not used to wait at the door, which will make the aforementioned waiting period into a source of irritation. In addition, if a large number of doors is to be opened every day the unlocking process must be smooth and easy.
Hence, it must be regarded as a qualified technical problem to reduce the time that lapses from the lock's detection of a nearby electronic key until the unlocking of the lock, or more particularly the delay that a user may experience waiting in front of the lock for it to unlock.
A natural way for the skilled person to solve this problem would be to increase the transmission power of the Bluetooth™ transceivers in the lock and key, since this would broaden the operating range thereof and allow earlier detection of an approaching key by the lock (such that the key will be detected already when the approaching user is at e.g. a 20 meter distance from the lock instead of e.g. a 10 meter distance), wherein the two-way link establishment may be initiated sooner and possibly be completed at the time when the user has reached the lock.
However, this solution has two pronounced drawbacks. First of all, the increased transmission power has an immediate penalty in the form of an increase in electric power consumption, which is particularly disadvantageous for battery-powered locks and keys. Secondly, the broadened operating range invites also other locks than the intended one to detect and interact with the key—in other words, the risk of cross-talk is increased.
In summary, there is a need for a flexible lock system arranged to work in situations with many users and many doors, and with a faster unlocking process.